SSINS No: 6835
IN 86-39
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
Washington, DC 20555
May 20, 1986
Information Notice No. NO 86-39: FAILURES OF RHR PUMP MOTORS AND PUMP
INTERNALS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP)
Purpose:
This notice is provided to alert licensees to serious damage which has
occurred at a licensed nuclear power plant to residual heat removal (RHR)
pumps manufactured by Bingham-Willamette with motors supplied by General
Electric The damage identified at the Philadelphia Electric Co (PECO),
Peach Bottom facility involved failure of motor bearings and/or failure of
pump impeller wear rings
It is expected that recipients will review this notice for applicability to
their facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities However, suggestions contained in
this notice do not constitute requirements; therefore, no specific action or
written response is required
Description of Circumstances:
On November 2, 1985, during core reload of PECO's Peach Bottom Unit 3, a
fire occurred in the 3C RHR pump motor which totally engulfed the motor and
rendered the pump inoperable A lower guide bearing high temperature alarm
had been received for 3 days prior to the pump failure, but this warning of
potential pump failure went unnoticed by personnel because of the large
number of other alarms that were received during the shutdown The motor, a
2000 HP GE vertical induction model 5K6348XC29, and pump, a
Bingham-Willamette single stage centrifugal model 18x24x28 CVIC (Figure 1),
were uncoupled, disassembled and inspected for damage Results of the
inspection identified that the motor lower guide bearing was destroyed, the
rotor bars were gouged and scorched, and the stator windings were burned and
gouged The pump internals were found to have sustained internal damage
Specifically, the lower impeller wear ring (Figure 1) was separated from the
impeller and fused to the casing wear ring No other wear surfaces indicated
wear or damage On November 16, 1985, while replacing the lower pump casing
gasket on the 3A RHR pump, PECO personnel discovered that the lower pump
impeller wear ring was separated from the impeller and cracked in three
places Subsequent inspections of the remaining two unit 3 RHR pumps and two
unit 2 pumps (2A and 2C) revealed similar wear ring failures in three of the
pumps inspected
IN 86-39
May 20, 1986
Page 2 of 3
On December 22, 1985, after several overcurrent alarms with pump 2D from
Unit 2, PECO inspected this pump and discovered the lower pump impeller wear
ring separated and cracked, a 6-inch piece of wear ring missing, and the
impeller vanes damaged Not all failures noted above were as severe as the
ones identified on pumps 3C and 2D However, the similarity was evident
The RHR pump impeller wear rings are press fit to the impeller and attached
with eight dowel pins The wear rings provide a wearing surface on the pump
impeller The wear rings are 410 stainless steel, A 182 grade F6 with a
Rockwell C hardness of 33 to 39 Metallurgical examinations of the wear ring
fracture surfaces indicate the presence of intergranular stress corrosion
cracking (IGSCC) PECO has classified the wear ring failures as IGSCC On
November 26, 1985, PECO made an INPO Network notification regarding these
RHR pump failures PECO has repaired all affected pumps by replacement of
damaged motors and pump internals Tennessee Valley Authority's Browns Ferry
Units 1, 2, and 3 utilize the identical pumps for RHR service Similar motor
and pump impeller wear ring failures have occurred at these facilities, but
not to the extent identified at Peach Bottom Pumps of similar design, but
different size, are utilized for core spray service both at Peach Bottom and
Browns Ferry However, these pumps use the "integral" impeller wear ring
design, ie , extended impeller part replaces separate wear ring and forms
a single unit, and therefore are not susceptible to the type of wear ring
failure previously described
Discussion:
These multiple events are of concern because of the potential for commonmode
failures of all pumps in the same system At Peach Bottom, six of eight
pumps inspected exhibited degraded pump impeller wear rings and internals
These flaws could lead to pump hydraulic degradation and, under the worst
conditions, complete pump failure The motor guide bearing failures are
significant because they could cause failure of the pump motors and pump
internal damage
The full extent to which this type of pump may be used in safety-related
services at other facilities is not known with complete certainty According
to information ascertained from Bingham-Williamette records and confirmed by
contact with affected sites, other plants utilizing this type of pump in the
RHR system include the following: Cooper, Pilgrim 1, and Vermont Yankee
The exact cause of the pump internal failures has not been fully determined,
except that there is evidence that IGSCC has contributed to the impeller
wear ring failures Operating pumps with inadequate flow and lubrication,
whereby high internal temperatures develop, is also a likely contributor,
eg, pump cavitation PECO is continuing to pursue root causes and wear
ring redesigns to prevent such occurrences in the future
IN 86-39
May 20, 1986
Page 3 of 3
No specific action or written response is required by this information
notice If you have any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or the
technical contact listed below
Edward L Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Ronald M Young
(301) 492-8985
Attachments:
1 Figure 1 - Typical CVIC RHR Pump
Sectional Assembly
2 List of Recently Issued IE Information Notices